Repeat: Difference between revisions
(+Stata) |
|||
Line 894: | Line 894: | ||
repeat(example, 4);</lang> |
repeat(example, 4);</lang> |
||
=={{header|Stata}}== |
|||
<lang stata>function repeat(f,n) { |
|||
for (i=1; i<=n; i++) (*f)() |
|||
} |
|||
function hello() { |
|||
printf("Hello\n") |
|||
} |
|||
repeat(&hello(),3)</lang> |
|||
=={{header|Swift}}== |
=={{header|Swift}}== |
Revision as of 23:22, 15 December 2017
- Task
Write a procedure which accepts as arguments another procedure and a positive integer.
The latter procedure is executed a number of times equal to the accepted integer.
Ada
<lang Ada>with Ada.Text_IO;
procedure Repeat_Example is
procedure Repeat(P: access Procedure; Reps: Natural) is begin for I in 1 .. Reps loop
P.all; -- P points to a procedure, and P.all actually calls that procedure
end loop; end Repeat; procedure Hello is begin Ada.Text_IO.Put("Hello! "); end Hello;
begin
Repeat(Hello'Access, 3); -- Hello'Access points to the procedure Hello
end Repeat_Example;</lang>
Output:
Hello! Hello! Hello!
ALGOL 68
<lang algol68>
- operator that executes a procedure the specified number of times #
OP REPEAT = ( INT count, PROC VOID routine )VOID:
TO count DO routine OD;
- make REPEAT a low priority operater #
PRIO REPEAT = 1;
- can also create variant that passes the iteration count as a parameter #
OP REPEAT = ( INT count, PROC( INT )VOID routine )VOID:
FOR iteration TO count DO routine( iteration ) OD;
main: (
# PROC to test the REPEAT operator with # PROC say something = VOID: print( ( "something", newline ) );
3 REPEAT say something;
# PROC to test the variant # PROC show squares = ( INT n )VOID: print( ( n, n * n, newline ) );
3 REPEAT show squares
) </lang> Output:
something something something +1 +1 +2 +4 +3 +9
Applesoft BASIC
http://hoop-la.ca/apple2/2016/winterwarmup/#repeat.bas
AutoHotkey
<lang AutoHotkey>repeat("fMsgBox",3) return
repeat(f, n){ loop % n %f%() }
fMsgBox(){ MsgBox hello }</lang>
AWK
<lang AWK>
- syntax: GAWK -f REPEAT.AWK
BEGIN {
for (i=0; i<=3; i++) { f = (i % 2 == 0) ? "even" : "odd" @f(i) # indirect function call } exit(0)
} function even(n, i) {
for (i=1; i<=n; i++) { printf("inside even %d\n",n) }
} function odd(n, i) {
for (i=1; i<=n; i++) { printf("inside odd %d\n",n) }
} </lang>
output:
inside odd 1 inside even 2 inside even 2 inside odd 3 inside odd 3 inside odd 3
Batch File
<lang dos> @echo off
- _main
setlocal call:_func1 _func2 3 pause>nul exit/b
- _func1
setlocal enabledelayedexpansion for /l %%i in (1,1,%2) do call:%1 exit /b
- _func2
setlocal echo _func2 has been executed exit /b </lang>
C
<lang c>#include <stdio.h>
void repeat(void (*f)(void), unsigned int n) {
while (n-->0) (*f)(); //or just f()
}
void example() {
printf("Example\n");
}
int main(int argc, char *argv[]) {
repeat(example, 4); return 0;
} </lang>
C++
<lang cpp>template <typename Function> void repeat(Function f, unsigned int n) {
for(unsigned int i=n; 0<i; i--) f();
}</lang> usage: <lang cpp>#include <iostream> void example() {
std::cout << "Example\n";
}
repeat(example, 4);</lang>
<lang cpp> repeat([]{std::cout << "Example\n";}, 4);</lang>
Clojure
<lang clojure>(defn repeat-function [f n]
(dotimes [i n] (f)))</lang>
- Output:
user=> (repeat-function #(println "bork") 3) bork bork bork
Common Lisp
<lang lisp>(defun repeat (f n)
(dotimes (i n) (funcall f)))
(repeat (lambda () (format T "Example~%")) 5)</lang>
D
<lang d>void repeat(void function() fun, in uint times) {
foreach (immutable _; 0 .. times) fun();
}
void procedure() {
import std.stdio; "Example".writeln;
}
void main() {
repeat(&procedure, 3);
}</lang>
- Output:
Example Example Example
EchoLisp
<lang lisp> (define (repeat f n) (for ((i n)) (f)))
(repeat (lambda () (write (random 1000))) 5)
→ 287 798 930 989 794
- Remark
- It is also possible to iterate a function
- f(f(f(f( ..(f x)))))
(define cos10 (iterate cos 10) (define cos100 (iterate cos10 10)) (cos100 0.6)
→ 0.7390851332151605
(cos 0.7390851332151605)
→ 0.7390851332151608 ;; fixed point found
</lang>
Forth
<lang forth>: times ( xt n -- )
0 ?do dup execute loop drop ;</lang>
Or, taking care to keep the data stack clean for the XT's use, as is often desired:
<lang forth>: times { xt n -- }
n 0 ?do xt execute loop ;</lang>
Or as a novel control structure, which is not demanded by this task but which is just as idiomatic in Forth as the XT-consuming alternatives above:
<lang forth>: times[ ]] 0 ?do [[ ; immediate compile-only
- ]times postpone loop ; immediate compile-only</lang>
Usage:
<lang forth>[: cr ." Hello" ;] 3 times
- 3-byes ( -- ) 3 times[ cr ." Bye" ]times ;
3-byes</lang>
- Output:
HelloHello Hello Bye Bye
Bye
FreeBASIC
<lang freebasic>' FB 1.05.0 Win64
Sub proc()
Print " proc called"
End Sub
Sub repeat(s As Sub, n As UInteger)
For i As Integer = 1 To n Print Using "##"; i; s() Next
End Sub
repeat(@proc, 5) Print Print "Press any key to quit" Sleep</lang>
- Output:
1 proc called 2 proc called 3 proc called 4 proc called 5 proc called
Go
<lang go>package main
import "fmt"
func repeat(n int, f func()) {
for i := 0; i < n; i++ { f() }
}
func fn() {
fmt.Println("Example")
}
func main() {
repeat(4, fn)
}</lang>
Haskell
Such a function already exists <lang Haskell>import Control.Monad (replicateM_)
sampleFunction :: IO () sampleFunction = putStrLn "a"
main = replicateM_ 5 sampleFunction</lang>
J
<lang J>
NB. ^: (J's power conjunction) repeatedly evaluates a verb.
NB. Appending to a vector the sum of the most recent NB. 2 items can generate the Fibonacci sequence.
(, [: +/ _2&{.) (^:4) 0 1
0 1 1 2 3 5
NB. Repeat an infinite number of times NB. computes the stable point at convergence
cosine =: 2&o.
cosine (^:_ ) 2 NB. 2 is the initial value
0.739085
cosine 0.739085 NB. demonstrate the stable point x==Cos(x)
0.739085
cosine^:(<_) 2 NB. show the convergence
2 _0.416147 0.914653 0.610065 0.819611 0.682506 0.775995 0.713725 0.755929 0.727635 0.74675 0.733901 0.742568 0.736735 0.740666 0.738019 0.739803 0.738602 0.739411 0.738866 0.739233 0.738986 0.739152 0.73904 0.739116 0.739065 0.739099 0.739076 0.739091 0.7...
# cosine^:(<_) 2 NB. iteration tallyft
78
f =: 3 :'smoutput hi'
f
hi
NB. pass verbs via a gerund repeat =: dyad def 'for_i. i.y do. (x`:0)0 end. EMPTY'
(f`)repeat 4
hi hi hi hi
NB. pass a verb directly to an adverb
Repeat =: adverb def 'for_i. i.y do. u 0 end. EMPTY'
f Repeat 4
hi hi hi hi </lang>
Java
<lang java>import java.util.function.Consumer; import java.util.stream.IntStream;
public class Repeat {
public static void main(String[] args) { repeat(3, (x) -> System.out.println("Example " + x)); }
static void repeat (int n, Consumer<Integer> fun) { IntStream.range(0, n).forEach(i -> fun.accept(i + 1)); }
}</lang>
Output:
Example 1 Example 2 Example 3
jq
We first define "repeat" naively but in accordance with the task specification; we then define an optimized version that illustrates a general technique for taking advantage of jq's support for tail-call optimization (TCO).
Since jq is a purely functional language, repeat(f; n) is unlikely to be very useful so we define a similar filter, repeatedly(f; n), which generates n+1 terms: . (the input), f, f|f, ... ; that is, using conventional functional notation, it generates: x, f(x), f(f(x)), ...
Unoptimized version: <lang jq>def unoptimized_repeat(f; n):
if n <= 0 then empty else f, repeat(f; n-1) end;</lang>
Optimized for TCO: <lang jq>def repeat(f; n):
# state: [count, in] def r: if .[0] >= n then empty else (.[1] | f), (.[0] += 1 | r) end; [0, .] | r;</lang>
Variant: <lang jq># If n is a non-negative integer,
- then emit a stream of (n + 1) terms: ., f, f|f, f|f|f, ...
def repeatedly(f; n):
# state: [count, in] def r: if .[0] < 0 then empty else .[1], ([.[0] - 1, (.[1] | f)] | r) end; [n, .] | r;</lang>
Examples: <lang jq>0 | [ repeat(.+1; 3) ]</lang> produces: [1,1,1] <lang jq>0 | repeatedly(.+1; 3)</lang> produces:
0 1 2 3
Julia
<lang julia>function sayHi() println("Hi") end
function rep(f, n) for i = 1:n f() end end
rep(sayHi, 3)</lang>
- Output:
Hi Hi Hi
Kotlin
<lang scala>// version 1.0.6
fun repeat(n: Int, f: () -> Unit) {
for (i in 1..n) { f() println(i) }
}
fun main(args: Array<String>) {
repeat(5) { print("Example ") }
}</lang>
- Output:
Example 1 Example 2 Example 3 Example 4 Example 5
LiveCode
<lang LiveCode>rep "answer",3
command rep x,n
repeat n times do merge("x n") end repeat
end rep</lang>
Lua
No particular magic required as Lua allows functions to be passed as arguments. <lang Lua>function myFunc ()
print("Sure looks like a function in here...")
end
function rep (func, times)
for count = 1, times do func() end
end
rep(myFunc, 4) </lang>
- Output:
Sure looks like a function in here... Sure looks like a function in here... Sure looks like a function in here... Sure looks like a function in here...
Mathematica
Note that anything of this form is not considered good practice. <lang Mathematica>repeat[f_, n_] := Do[f[], {n}]; repeat[Print["Hello, world!"] &, 5];</lang>
- Output:
Hello, world! Hello, world! Hello, world! Hello, world! Hello, world!
МК-61/52
<lang>1 П4
3 ^ 1 6 ПП 09 С/П
П7 <-> П0 КПП7 L0 12 В/О
ИП4 С/П КИП4 В/О</lang>
Objeck
<lang objeck>class Repeat {
function : Main(args : String[]) ~ Nil { Repeat(Example() ~ Nil, 3); } function : Repeat(e : () ~ Nil, i : Int) ~ Nil { while(i-- > 0) { e(); }; } function : Example() ~ Nil { "Example"->PrintLine(); }
}</lang>
OCaml
<lang ocaml>let repeat ~f ~n =
for i = 1 to n do f () done
let func () =
print_endline "Example"
let () =
repeat ~n:4 ~f:func
</lang>
Oforth
This method is already defined : times. This method can be used on all runnables (functions, methods, blocks, ...).
<lang Oforth>: hello "Hello, World!" println ; 10 #hello times</lang>
- Output:
Hello, World! Hello, World! Hello, World! Hello, World! Hello, World! Hello, World! Hello, World! Hello, World! Hello, World! Hello, World!
PARI/GP
<lang parigp>repeat(f, n)=for(i=1,n,f()); repeat( ()->print("Hi!"), 2);</lang>
- Output:
Hi! Hi!
Perl
<lang perl>sub repeat {
my ($sub, $n) = @_; $sub->() for 1..$n;
}
sub example {
print "Example\n";
}
repeat(\&example, 4);</lang>
Perl 6
<lang perl6>sub repeat (&f, $n) { f() xx $n };
sub example { say rand }
repeat(&example, 3);</lang>
- Output:
0.435249779778396 0.647701200726486 0.279289335968417
Of course, we could have just written
example() xx 3;
or even
(say rand) xx 3;
directly – the custom repeat
subroutine is just here to satisfy the task description.
Notes on the xx
operator:
- Unlike other operators, it evaluates its left-hand-side argument lazily - that's why we can simply call
f()
there rather than passing it as a function object. - The operator has a return value: A list consisting of the return values of the left-hand-side (and building lists is in fact what
xx
is usually used for).
General notes:
- The
&
sigil in therepeat
subroutine signature restricts that parameter to types that implement theCallable
role, and makes it available inside therepeat
subroutine body as if it were a lexically scoped sub. - The parentheses in the last line are necessary to disambiguate it as a call to our custom subroutine, rather than an attempt to use the built-in
repeat { ... } while ...
construct.
Phix
<lang Phix>procedure Repeat(integer rid, integer n)
for i=1 to n do call_proc(rid,{}) end for
end procedure
procedure Hello()
?"Hello"
end procedure
Repeat(routine_id("Hello"),5)</lang>
PicoLisp
<lang PicoLisp># The built-in function "do" can be used to achieve our goal,
- however, it has a slightly different syntax than what the
- problem specifies.
- Native solution.
(do 10 (version))
- Our solution.
(de dofn (Fn N)
(do N (Fn)) )
(dofn version 10)</lang>
PowerShell
(Made more PowerShelly.)
<lang PowerShell> function Out-Example {
"Example"
}
function Step-Function ([string]$Function, [int]$Repeat) {
for ($i = 1; $i -le $Repeat; $i++) { "$(Invoke-Expression -Command $Function) $i" }
}
Step-Function Out-Example -Repeat 3 </lang>
- Output:
Example 1 Example 2 Example 3
Python
<lang Python>#!/usr/bin/python def repeat(f,n):
for i in range(n): f();
def procedure():
print("Example");
repeat(procedure,3); #prints "Example" (without quotes) three times, separated by newlines.</lang>
R
<lang R> f1 <- function(...){print("coucou")}
f2 <-function(f,n){ lapply(seq_len(n),eval(f)) }
f2(f1,4) </lang>
Racket
The racket guide has a section called "Iterators and Comprehensions", which shows that for isn't just for repeating n times!
<lang Racket>#lang racket/base (define (repeat f n) ; the for loop is idiomatic of (although not exclusive to) racket
(for ((_ n)) (f)))
(define (repeat2 f n) ; This is a bit more "functional programmingy"
(when (positive? n) (f) (repeat2 f (sub1 n))))
(display "...") (repeat (λ () (display " and over")) 5) (display "...") (repeat2 (λ () (display " & over")) 5) (newline)</lang>
- Output:
... and over and over and over and over and over... & over & over & over & over & over
REXX
The procedure name (that is being repeatedly executed) isn't restricted to an internal REXX subroutine (procedure),
it may be an external program (procedure) written in any language.
<lang rexx>/*REXX program executes a named procedure a specified number of times. */
parse arg pN # . /*obtain optional arguments from the CL*/
if #== | #=="," then #=1 /*assume once if not specified. */
if pN\== then call repeats pN, # /*invoke the REPEATS procedure for pN.*/
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
repeats: procedure; parse arg x,n /*obtain the procedureName & # of times*/
do n; interpret 'CALL' x; end /*repeat the invocation N times. */ return /*return to invoker of the REPEATS proc*/
/*──────────────────────────────────────────────────────────────────────────────────────*/ yabba: say 'Yabba, yabba do!'; return /*simple code; no need for PROCEDURE.*/</lang> output when the input is: yabba 4
Yabba, yabba do! Yabba, yabba do! Yabba, yabba do! Yabba, yabba do!
output when the input is: $date 3
[The (external) $DATE.REX program isn't supplied here.]
day-of-year= 159 Gregorian date= 06/08/2014 Sunday day-of-year= 159 Gregorian date= 06/08/2014 Sunday day-of-year= 159 Gregorian date= 06/08/2014 Sunday
Ring
<lang ring> Func Main
times(5,:test)
Func Test
see "Message from the test function!" + nl
Func Times nCount, F
for x = 1 to nCount Call F() next
</lang>
Ruby
<lang ruby>4.times{ puts "Example" } # idiomatic way
def repeat(proc,num)
num.times{ proc.call }
end
repeat(->{ puts "Example" }, 4)</lang>
Rust
<lang rust>// Repeat the function f, n times. fn repeat<F>(f: &F, n: u32)
where F: Fn() { for _ in 0..n { f(); }
}
fn static_fn() {
print!("Static ");
}
fn main() {
// Repeat a static function. repeat(&static_fn, 4);
println!("");
// Repeat an anonymous closure. repeat(&|| print!("Closure "), 5);
}</lang>
- Output:
Static Static Static Static Closure Closure Closure Closure Closure
Scala
Intuitive solution
- Call by name
- Type parameterization
- Higher order function
<lang scala> def repeat[A](n:Int)(f: => A)= ( 0 until n).foreach(_ => f)
repeat(3) { println("Example") }</lang>
Advanced Scala-ish
- Call by name
- Type parameterization
- Implicit method
- Tail recursion
- Infix notation
<lang scala>object Repeat2 extends App {
implicit class IntWithTimes(x: Int) { def times[A](f: => A):Unit = { @tailrec def loop( current: Int): Unit = if (current > 0) { f loop(current - 1) } loop(x) } }
5 times println("ha") // Not recommended infix for 5.times(println("ha")) aka dot notation
}</lang>
Most Scala-ish
- Call by name
- Type parameterization
- Implicit method
- Tail recursion
- Infix notation
- Operator overloading
<lang scala>import scala.annotation.tailrec
object Repeat3 extends App {
implicit class UnitWithNtimes(f: => Unit) { def *[A](n: Int): Unit = { // Symbol * used instead of literal method name @tailrec def loop(current: Int): Unit = if (current > 0) { f loop(current - 1) } loop(n) } }
print("ha") * 5 // * is the method, effective should be A.*(5)
}</lang>
Scheme
Scheme is mostly made up from expressions which return values. However some functions, such as display, return an unspecified value. The actual value returned varies depending on the Scheme implementation itself.
<lang scheme> (import (scheme base)
(scheme write))
(define (repeat proc n)
(do ((i 0 (+ 1 i)) (res '() (cons (proc) res))) ((= i n) res)))
- example returning an unspecified value
(display (repeat (lambda () (display "hi\n")) 4)) (newline)
- example returning a number
(display (repeat (lambda () (+ 1 2)) 5)) (newline) </lang>
- Output:
(Using chibi-scheme: returns #<undef> from display.)
hi hi hi hi (#<undef> #<undef> #<undef> #<undef>) (3 3 3 3 3)
Sidef
<lang ruby>func repeat(f, n) {
{ f() } * n;
}
func example {
say "Example";
}
repeat(example, 4);</lang>
Stata
<lang stata>function repeat(f,n) { for (i=1; i<=n; i++) (*f)() }
function hello() { printf("Hello\n") }
repeat(&hello(),3)</lang>
Swift
<lang swift>func repeat(n: Int, f: () -> ()) {
for _ in 0..<n { f() }
}
repeat(4) { println("Example") }</lang>
Tcl
The usual way of doing a repeat would be: <lang tcl>proc repeat {command count} {
for {set i 0} {$i < $count} {incr i} { uplevel 1 $command }
}
proc example {} {puts "This is an example"}
repeat example 4</lang>
However, the time
command can be used as long as the return value (the report on the timing information) is ignored.
<lang tcl>time example 4</lang>
It should be noted that the “command” can be an arbitrary script, not just a call to a procedure:
<lang tcl>repeat {puts "hello world"} 3</lang>
Ursa
<lang ursa>def repeat (function f, int n) for (set n n) (> n 0) (dec n) f end for end repeat
def procedure () out "Hello! " console end procedure
- outputs "Hello! " 5 times
repeat procedure 5</lang>
XLISP
<lang lisp>(defun repeat (f n)
(f) (if (> n 1) (repeat f (- n 1)) ) )
- an example to test it
(repeat (lambda () (print '(hello rosetta code))) 5)</lang>
- Output:
(HELLO ROSETTA CODE) (HELLO ROSETTA CODE) (HELLO ROSETTA CODE) (HELLO ROSETTA CODE) (HELLO ROSETTA CODE)
zkl
<lang zkl>fcn repeat(f,n){ do(n){ f() } } repeat("ho ".print,3);</lang>
- Output:
ho ho ho
- Draft Programming Tasks
- Ada
- ALGOL 68
- Applesoft BASIC
- AutoHotkey
- AWK
- Batch File
- C
- C++
- Clojure
- Common Lisp
- D
- EchoLisp
- Forth
- FreeBASIC
- Go
- Haskell
- J
- Java
- Jq
- Julia
- Kotlin
- LiveCode
- Lua
- Mathematica
- МК-61/52
- Objeck
- OCaml
- Oforth
- PARI/GP
- Perl
- Perl 6
- Phix
- PicoLisp
- PowerShell
- Python
- R
- Racket
- REXX
- Ring
- Ruby
- Rust
- Scala
- Scheme
- Sidef
- Stata
- Swift
- Tcl
- Ursa
- XLISP
- Zkl